What is this circuit section doing??

[armdnrdy]

Good news indeed!

The problems you are encountering are all fixable.

The balance trimmer before the 5088 is the BBD output trimmer. You really won't hear much of a difference when you adjust it.

The BBD output trimmer needs to be adjusted with a scope. You put the scope lead on the trimmers wiper and move the trimmer until the two BBD output signals perfectly overlap into one signal. There are other easier ways to achieve this output mixing with resistors....but IMO this is the best way.

Did you add the BBD output level trimmer at the emitter of the 5088? Right now the signal is being boosted too much for the surrounding circuitry. The signal is making it's way to the output of the NE571 then going two different directions. The signals going to the output and to the feedback circuit. That's why it's oscillating. The trimmer (it's on the Mutron Flanger 3007 drawing that I did) will allow you to roll back the signal.

Oh...and thanks for the voltages Dino!

[digi2t]

Did you add the BBD output level trimmer at the emitter of the 5088?

There already is a 10K trimmer (R21) on the original, so I'm using that one.

[armdnrdy]

Did you add the BBD output level trimmer at the emitter of the 5088?

There already is a 10K trimmer (R21) on the original, so I'm using that one.

Do you mean R80? The trimmer that's connected to the second SAD section output?
If that's the trimmer your referring to, that is the output pull down trimmer. That won't affect level. Notice how the BBDs output pins 5 & 6 are connected, uninterrupted to the filter, 571, then output.

You need a trimmer connected to the emitter, the other side of the trimmer connected to ground, and the wiper to the remaining output signal path.

Update 

I just looked at the other thread and I see that I gave you the advise the original trimmer would work.
Well it will.....if configured the right way.
The original trimmer has lug 3 left floating (not connected) you need to tack a jumper to the unused lug and attach that to the 5088 emitter. You can't use the SAD's socket pins 5 & 6 for the BBDs output because they are connected to the trimmer. You need to get the 3007s outputs (with pull up resistors) to the base of the 5088.

Have you ever noticed that sometimes everything seems to be a big PITA! 

[digi2t]

Damn, I didn't notice the configuration. My bad. I'll reconfigure it tonight, and try it again.

Do you think that I'll need the two 4.7K resistors on T1?

[armdnrdy]

Do you think that I'll need the two 4.7K resistors on T1?

No....The two 4.7K resistors are there as a voltage divider just to "zero" in on the useful bias voltage. Without them the trimmer can go all the way from 0 volts (GND) to 15 volts.
With the resistors you have around 7.5 volts centered with a swing from 3.63 to 11.36 volts. Much more useful for bias voltage.

I hate to ask....but do you think you can take the LDR voltages again?
I should have been more clear on the subject.
If you look at the schematic, you'll see that all of the components in the foot pedal control circuit go back to "power" ground.


After reviewing the voltages you took, it seems as if you took them from the points I specified to signal ground.
Signal ground is actually a reference voltage so the voltage points to signal ground will give different readings. (negative, 1/2 voltage for +V, 1/2 voltage to ground)

A couple of the voltages I can transpose, but the negative voltages kind of got me.
When these voltage points are taken to power ground there won't be any negative voltages.

[digi2t]

You`re absolutely correct, I did connect to the signal ground (output jack ground). I`ll take the readings again tonight.

Noob question running through my mind here; Even with the negative voltage readings I gave, considering the signal ground sits in the middle of +/-7.5v, would it be logical to assume that we can add the recorded voltages to the + reference voltages to get the real voltages? Guess I`ll get my answer to that tonight.

[armdnrdy]

Noob question running through my mind here; Even with the negative voltage readings I gave, considering the signal ground sits in the middle of +/-7.5v, would it be logical to assume that we can add the recorded voltages to the + reference voltages to get the real voltages? Guess I`ll get my answer to that tonight.

Definitely,
but for some reason between work and all of the other projects that I'm working on...my brain seems to be exhibiting a loss in the forward/backward/negative/positive region!
Read as: can't wrap my mind around it! 

[Ronan]

Here you go:
0V to signal ground is 7.58V
toe up 7.58 - 5.35 = 2.23V
toe down 7.58 + 4.31 = 11.89V
Resistance of LDR 2 at toe down position approx 5.3 Megohms.

If the voltage across LDR 1 (PC1) does not change with treadle position, then that confirms that PC1's only purpose in life is to help maintain the light output from the LED CR18 at a constant brightness.

[armdnrdy]

Thanks for the brain power Ian!

I have to recharge my mental batteries!

I first saw those numbers this morning before my first sip of coffee and my brain said, "Sorry....I don't think so!"

[digi2t]

Here you go:
0V to signal ground is 7.58V
toe up 7.58 - 5.35 = 2.23V
toe down 7.58 + 4.31 = 11.89V
Resistance of LDR 2 at toe down position approx 5.3 Megohms.

If the voltage across LDR 1 (PC1) does not change with treadle position, then that confirms that PC1's only purpose in life is to help maintain the light output from the LED CR18 at a constant brightness.

Confirmation on the numbers. Just as Ian has stated. No change on the numbers for the other LDR (facing the LED), a steady 5.50 volts on one lead, and 15 volts on the other.

Also, I modded the daughterboard, by lifting the number 6 pin of the SAD1024 adapter, and connecting the existing 10K trimmers free leg to the 2N5088 emitter.

SUCCESS!!!!
I readjusted the bias and output, and it sounds pretty much like it does with the SAD1024. I pulled the daughterboard out, popped the SAD1024 back in, and readjusted... yup, same sound. Absolutely smashing, I say! We're good to go with the MN3007, as drawn, minus the 4.7K resistors around T1. (Cue the marching band.)

Sorry, no video proof. The wife is gone on vacation, and she's got the camera.

[armdnrdy]

I just don't have the words! 

I am overcome with joy!

Okay, I have regained composure.

Great work! Now we can forge ahead!

[digi2t]

Thanks. It just impressed the hell out of me that it worked. I can't put into words how humbling it is to be working with some great brain power here. I just wish I had been a bit smarter back in the day, and stayed in school longer. Oh well... a late start is better than no start at all.

When I get the camera back, I'll shoot some pics of the daughterboard, after a make a small mod for connecting to the output trimmer. It's low enough to plug into the socket of the SAD, and fit between the board and the enclosure. Could be a nice retrofit for a Mutron with an SAD that's kaput.

[armdnrdy]

Yes....this is good!

Sketch up a schematic and I'll draw it up all nice like if you don't have the time.

[armdnrdy]

I worked up some calculations from the voltages taken at the LDR (PC2) and IC10 test points. From that info and the known resistance values and voltage, I was able to calculate the specs of the LDR's dark resistance and light resistance.

[digi2t]

Finally got a couple of pics of the daughterboard. Here ya go...

[armdnrdy]

It's ALIVE! 

Great job Dino!

[digi2t]

Here's the final layout of the daughterboard;



and the schematic;



Thanks Larry!

[pinkjimiphoton]

I @#$%ING LOVE YOU GUYS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
THANK YOU!!!!!!!!!